Reduction in size and weight has been demanded as corresponding to advancing portabilization of electric and electronic equipment such as PCs, office automation equipment, audio-visual equipment, cell-phones, telephones, facsimile machines, home electric appliances and toys. To meet the demand, sheet thinning is required together with high strength and high rigidity so that equipment component parts such as a housing is prevented from greatly bending to contact and break inner component parts even when an external load is applied.
Further, a shaped product having an upright part such as a rib and boss may be formed by filling a rib-forming part with reinforced fibers or filling it with mat-shaped reinforcing fibers in shaping the product. In the former case, thermoplastic resin base material containing randomly-oriented discontinuous reinforcing fibers is usually employed to perform a press forming, which may be difficult to achieve otherwise.
The rib may be formed in a forming mold by filling the rib-forming part with flowable base material and consists of reinforcing fibers and matrix resin made of thermoplastic resin when the base material is subject to press forming with the forming mold. It is important that a complicated shape of the rib or the like should be formed precisely by the pressing to sufficiently fill the rib-forming part with the reinforcing fibers without generating resin-rich parts.
A sandwich structure consisting of a light core layer and rigid skin layer may be used for sheet thinning. It is important to provide a shaped product having a competitive cost as a universal housing for electronic component parts by forming an upright part having high strength and complicated shape such as a rib projecting in an out-of-plane direction of the skin layer by a simple method such as a one-motion forming method.
JP2012-148443-A discloses a configuration and an advantage, the configuration being that “a material is subject to a press working in a mold to make a rib while another material is melt in another mold and is subject to a pressing working to make a panel, the rib is heated at a temperature higher than the melting point of the thermoplastic resin, the another mold is once opened to place the heated rib on the panel, and then the another mold is closed again to perform a press working to provide fiber reinforced resin material having a ribbed structure, wherein a weight average fiber length content of the material to form the rib is less than that of the another material to form the panel,” the advantage is that “the ribbed panel made of fiber reinforced resin is effectively prevented from generating sink on a surface of the panel opposite to a ribbed surface.”
Although JP '443 discloses a method of integrating by press working the rib-forming part and the other parts which have been formed separately in each mold, the reinforcing fibers might not achieve sufficient reinforcement because a break or an interface tends to remain in the reinforcing fibers existing at a boundary part of both formed parts. Further, fluidity of the forming material itself cannot be utilized because both parts have been formed before press working and therefore materials are not likely to flow greatly between both parts at press working although the fluidity is supposed to be exhibited as excellent when a whole material is integrated by a press working. Therefore, it may become difficult to perform a desired three-dimensional shape easily.
JP2014-172241-A discloses a configuration and an advantage, the configuration being that “a shaped product, which has at least one upright part which is pressed and formed as projecting from a plane-forming part in an out-of-plane direction and comprises a first fiber reinforced thermoplastic resin layer and a second fiber reinforced thermoplastic resin layer laminated on at least one surface thereof, the first fiber reinforced thermoplastic resin layer having a first reinforcing fiber layer in which reinforcing fibers are randomly-oriented, the second fiber reinforced thermoplastic resin layer having a second reinforcing fiber layer, the second fiber reinforced thermoplastic resin layer being ruptured at the upright part while the first reinforcing fiber layer continuously extends between the plane-forming part and an inside of the upright part,” the advantage being that “the reinforcing resin can sufficiently reinforce the product without generating substantive boundary between the plane-shaped part and the inside of the upright part because the reinforcing fiber layer continuously extends between the plane-forming part and an inside of the upright part”.
In the configuration disclosed in JP '241, the second fiber reinforced thermoplastic resin layer is ruptured at the upright part and the first reinforcing fiber layer of the first fiber reinforced thermoplastic resin layer continuously extends between the plane-forming part and an inside of the upright part through the ruptured part so that the second fiber reinforced thermoplastic resin layer may be too weak to function as a skin layer of sandwich structure such as housing requiring a high rigidity.
JP2013-176984-A discloses a configuration and an advantage, the configuration being that “a rib structure provided in a shaped product made by pressing a preform comprising a sheet-shaped forming material (A) having a concentration parameter above a predetermined level, discontinuous reinforcing fiber, thermoplastic resin and a sheet-shaped forming material (B) having a concentration parameter below a predetermined level with an open mold having an opening to form the rib structure and a counter mold facing thereof, wherein an area of the forming material (A) is set to 70% or more of a projection area of shaped product, the forming material (B) is placed at an opening position of the opening, the forming material (A) is placed between the forming material (B) and the open mold, and the forming material (A) has a penetration part in a projection region of the opening,” the advantage being that “a shaped product of fiber reinforced composite material achieving both formations of the rib structure and face plate part excellent in surface appearance, dimensional accuracy and reliability is obtained.”
In the configuration disclosed in JP '984, the penetration part of the forming material (A) has a width narrower than that of rib opening so that filling the rib-forming part with the forming material B should be improved. Further, the surface layer is made from the discontinuous reinforcing fibers and thermoplastic resin so that the surface layer should be improved in rigidity and strength.
It could therefore be helpful to provide a sandwich structure, shaped product, and production processes therefor, the sandwich structure and the shaped product being lightweight and having high strength and high rigidity, specifically with an upright part such as rib shaped easily and surely to have a desirable shape and strength, wherein the upright part having a complicated shape such as rib projecting in an out-of-plane direction of a skin layer can be formed by a simple method such as one-motion forming method.